Distribution constant, partitioning

This is the most direct and simple theory of chromatography. The transport of the solute down the column will depend upon the distribution constant (partition coefficient), K, and the ratio of the amounts of the two phases in the column. Band (zone) shape does not change during this movement through the column. The system could be visualized as illustrated in Figures 1.10, 1.11. 

Generally, the distribution constant (partition coefficient) as a function of temperature is the first measurement obtained in such a study since other constants may be derived from these data. The distribution constant, KD, is the ratio of a component in a single definite form in the stationary phase per unit volume to its concentration in the mobile phase per unit volume at equilibrium. 

According to chromatographic theory, the solute net (adjusted) retention volume Vr is related to the solute distribution constant (partition coefficient) K by the equation... 

DISTRIBUTION CONSTANT, PARTITION COEFFICIENT, AND DISTRIBUTION RATIO... 

If octanol is the stationary phase and water the mobile phase, Po/w is the octanol-water distribution constant (partition coefficient) without any assumption but with the condition that no chemical change can affect the... 

The constant K is termed the distribution or partition coefficient. As a very rough approximation the distribution coefficient may be assumed equal to the ratio of the solubilities in the two solvents. Organic compounds are usually relatively more soluble in organic solvents than in water, hence they may be extracted from aqueous solutions. If electrolytes, e.g., sodium chloride, are added to the aqueous solution, the solubility of the organic substance is lowered, i.e., it will be salted out this will assist the extraction of the organic compound. 

To understand the fundamental principles of extraction, the various terms used for expressing the effectiveness of a separation must first be considered. For a solute A distributed between two immiscible phases a and b, the Nernst Distribution (or Partition) Law states that, provided its molecular state is the same in both liquids and that the temperature is constant ... 

The initial retention of metals in all fractions was linearly dependent upon the loading levels (Figs. 6.1-6.4). This constant partition behavior was also maintained after one year of incubation, but the distribution among fractions had shifted. This behavior indicates that there is no saturation... 

Enantiomer distribution constant (EDC). Estimates in CDClj-rich layer in the partitioning of an equivalent of racemic host (H) and optically pure L-valine as guest (G) and their complexes between two liquid phases composed of RCO,D(H). CDC1 and 020"... 

Paschke, A. and Popp, P. 2003, Solid-phase microextraction fibre-water distribution constants of more hydrophobic organic compounds and dieir correlations widi octanol-water partition coefficients. J. Chromatogr. A 999 35-42. 

There is no internationally recommended symbol for the distribution constant, but the symbol P (for partition constant) is common usage in this context. Coordination (complex) chemists (as in Chapter 3) prefer the symbol K-o (for the German Tonstante for constant ) sometimes other symbols are used. The important point is that the symbol should be properly defined in the text. 

It was shown by Roux (1974) that the two ideal sites model applies perfectly to partitioning of Rb distribution between nepheline and hydrothermal solutions. Based on the experimental work of Roux (1974), deviation from ideality in the normalized Rb/Na distribution between nepheline (X.) and hydrothermal solution (Xaq) is detectable for X, values higher than 10 (figure 10.3A) Distribution constant Xin the Nemst s law range is Kq = 0.82 (Roux, 1974), and the modification of K with increasing X, is well described by equation 10.20, within experimental approximation (figure 10.3B). 

Equation 7.1 shows that the retention volume of a solufe can be used to estimate its distribution constant, or the partition coefficient in the liquid system used in the CCC colunm ... 

Equilibrium Partition Constants and Standard Free Energy of Transfer Effect of Temperature on Equilibrium Partitioning Using Linear Free Energy Relationships (LFERs) to Predict and/or to Evaluate Partition Constants and/or Partition Coefficients Box 3.2 Partition Constants, Partition Coefficients, and Distribution Ratios -A Few Comments on Nomenclature Concluding Remarks... 

Box. 3.2 Partition Constants, Partition Coefficients, and Distribution Ratios, A Few Comments on Nomenclature... 

An isotherm is a graphical presentation of the interaction of an adsorbent and a sorbate in solution (gas or liquid solvent) at a given temperature. The isotherm is a graphical representation of the partition coefficient or distribution constant, K... 

The linear isotherm is obtained when the ratio of the concentration of substance adsorbed per unit mass and the concentration of the substance in solution remains constant. This means the partition coefficient or distribution constant, K (see Section 1.4) is a constant over all working concentration ranges. Thus, the front and rear boundaries of the band or zone will be symmetrical. 

The distribution isotherms (representation of the partition coefficient or distribution constant, K) may be either linear... 

Both concentrations should be calculated per unit volume of the phase. The term "distribution constant" is recommended in preference to the term "partition coefficient" which has been used with the same definition. 

The most popular method for measuring the polarity of a solute entails determination of the distribution constant between water and a water-immiscible solvent, e.g., octanol. However, because there is difficulty in dissolving proteins in the solvent, a two-phase aqueous system was developed (Shanbhag and Axelson, 1975). Albertson (1986) reported the construction of various aqueous phase systems for partitioning proteins, other macromolecules, and even cells. Recently, simpler aqueous biphase systems were selected for hydrophobic partitioning of proteins (Hachem et al., 1996). However, because of restrictions similar to those for HIC, as discussed above, it may be premature to replace the method used in Basic Protocol 5. The definition of hydrophobicity is based on the polarity of chemical compounds, which is closely related to the distribution between solvents of different polarities. This theory is similar to the elution mechanism of phase distribution chromatography as well as phase partition. However, complexity in the partition system and procedure hampers the broad use of the phase partition approaches. 

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